Mechatronics Systems Engineering - Theses, Dissertations, and other Required Graduate Degree Essays

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Investigating the Local Membrane Degradation Mechanisms in PEM Fuel Cells

Date created: 
2014-02-27
Abstract: 

As fuel cell industry matures over the years, the reliability and durability issues of this state-of-the-art technology become of greater concern among the researchers of this field. Aiming at durability issues of fuel cells, this research has been dedicated to a novel experimental approach in analysis of local membrane degradation phenomena in PEMFCs, with the aim of shedding light on the potential effects of manufacturing imperfections on this process. Followed by a comprehensive review on historical membrane failure analysis data from Ballard Power Systems’ field operated MEAs, three distinct alternatives have been proposed as potential candidates for initiating or accelerating the local membrane degradation phenomena. Catalyst layer delaminations, catalyst cracks, and local sources of Fenton’s reagents are the three options investigated in the current study. Customized MEAs were designed, fabricated and tested under two different in-situ accelerated-stress-test conditions and extensive post mortem analysis has been done on the end-of-life samples. The observations suggested a significant accelerating effect for iron contamination on membrane degradation process in a global term, leading to remarkably shorter lifetimes, but dismissed the local traces of iron oxide as the local initiators or accelerators of this phenomenon. Studying the potential effects of catalyst-layer delamination revealed that having this defect on the anode side can lead to an extremely thinned membrane, while same anomaly, if placed on cathode catalyst-membrane interface has a negligible effect on the rate of membrane thinning under identical operating conditions. Moreover, a substantial mitigating effect for platinum remainders on the site of delamination has been observed on both tests. Eventually, looking at artificial catalyst layer cracks, it was verified that anode and cathode cracks could have no significant impact on local membrane degradation phenomena. While historically, a great deal of degradation studies has been focused on the cathode side, these findings, when considered as a whole, can change the way industries look at the degradation process. Concluded by these in-situ experiments, anode can actually be considered as a key player in the convoluted degradation process.

Document type: 
Thesis
File(s): 
Supervisor(s): 
Erik Kjeang
Gary Wang
Department: 
Applied Sciences: School of Mechatronic Systems Engineering
Thesis type: 
(Thesis) M.A.Sc.

Analysis of air flow distribution and thermal comfort in a hybrid electric vehicle

Author: 
Date created: 
2014-11-18
Abstract: 

Energy efficiency in Hybrid Electric Vehicles (HEV) affects the vehicle mileage and battery durability. Air conditioning is the most energy consuming system after the electric motor in HEVs. Air flow distribution and thermal comfort in an HEV is studied and simulations are performed to investigate the optimum air distribution pattern for providing thermal comfort while maintaining energy efficiency. To acquire a preliminary understanding of the problem, an analytical model is developed for air flow in a cavity. In the next step, a testbed is developed and different air conditioning scenarios are experimented. For numerical simulations, several turbulence models are verified with the experimental data and the realizable k-epsilon model is selected. After validation, the numerical model is applied to various air conditioning scenarios inside the eVaro cabin. It is concluded that optimum air distribution patterns exist for different thermal loads and personalized ventilation can improve energy efficiency by 30% when only driver is on board.

Document type: 
Thesis
File(s): 
Supervisor(s): 
Majid Bahrami
Department: 
Applied Sciences:
Thesis type: 
(Thesis) M.A.Sc.

Utilization of Internal Resonance in Gyroscope Design

Author: 
Date created: 
2014-11-26
Abstract: 

Coriolis vibratory gyroscopes (CVG) suffer from various error sources including manufacturing imperfections and environmental factors. Most design constraints incorporate having the drive and sense mode natural frequencies equal. This poses a difficult solution called “mode matching” requiring complex and extremely accurate on-chip electronics. The research discussed in this thesis acts as a proof of concept on utilizing well-established phenomena in the field of nonlinear dynamics and vibration in the design of CVG gyroscopes with improved stability against manufacturing imperfections. A significant increase in the sense mode bandwidth is shown by structurally tuning the system to 2:1 resonance between the sense and drive modes respectively. A simplified mathematical model of a two-degree-of-freedom system, having quadratic nonlinearities, is obtained and compared qualitatively to more complex models from literature. Experimental results verify numerical simulations, confirming the hypothesis. Additional bandwidth enhancement possibility is established through simple feedback of nonlinear coupling terms obtained from mathematical models.

Document type: 
Thesis
File(s): 
Supervisor(s): 
Farid Golnaraghi
Department: 
Applied Sciences: School of Mechatronic Systems Engineering
Thesis type: 
(Thesis) Ph.D.

Pushing the Limits of Natural Convection Heat Transfer from the Heatsinks

Author: 
Date created: 
2014-12-19
Abstract: 

This research, which has been done in close collaboration with industrial partners, Alpha Technologies and Analytic Systems companies, aims to push the current limits of natural convection heat transfer from vertical heatsinks, with application in passive thermal management of electronics and power electronics. Advantages such as; being noise-free, reliable, with no parasitic power demand, and less maintenance requirements, make passive cooling a preferred thermal management solution for electronics. The focus of this thesis is to design high performance naturally-cooled heatsinks, to increase the cooling capacity of available passive thermal management systems. Heatsinks with interrupted rectangular vertical fins are the target of this study. Due to the complexities associated with interrupted fins, interrupted rectangular single wall is chosen as the starting point of the project. Asymptotic solution and blending technique is used to present a compact correlation for average Nusselt number of such wall, for the first time. The proposed correlation is verified by the results obtained from numerical simulations, and experimental data obtained from a custom-designed testbed. In the next step, natural convection heat transfer from parallel plates has been investigated. Integral technique is used to solve the governing equations, and closed-form correlations for velocity, temperature, and local Nusselt number are developed for the first time. The results are successfully verified with the result of an independent numerical simulation and experimental data obtained from the tests conducted on heatsink sample. In the last step, to model heat transfer from interrupted finned heatsinks, and to obtain compact correlations for velocity and temperature inside the domain, an analytical approach is used. Numerical simulations are performed to provide the information required by our analytical approach. An extensive experimental study is also conducted to verify the results from analytical solution and numerical simulation. Results show that the new-designed heatsinks are capable of dissipating heat five times more than currently available naturally-cooled heatsinks, with a weight up to 30% less. The new heatsinks can increase the capacity of passive-cooled systems significantly.

Document type: 
Thesis
File(s): 
Supervisor(s): 
Majid Bahrami
Department: 
Applied Sciences:
Thesis type: 
(Thesis) Ph.D.

Metamodel-Based Global Optimization Methodologies for High Dimensional Expensive Black-box Problems

Date created: 
2014-12-04
Abstract: 

Many engineering problems involve high dimensional, computationally expensive, and black-box (HEB) functions such as complex finite element analyses or computational fluid dynamics simulations. Global optimization on HEB problems is challenging since it generally requires a large number of computationally expensive simulations. The aim of this thesis is to tackle optimization on HEB problems. Metamodels are mathematical models that are constructed to approximate black-box and expensive functions. Survey of existing techniques shows that metamodel-based optimization has potential to solve HEB optimization problems. High Dimensional Model Representation (HDMR) metamodeling is chosen from the literature, which is subsequently developed to Principal Component Analysis based HDMR in support of random non-uniform sampling. Also, an adaptively changing basis functions strategy is defined to ensure the orthogonality of basis functions with respect to existing samples in order to achieve the best approximation accuracy for Random Sampling HDMR. Variable correlations revealed through metamodeling are used for decomposing high dimensional problems into smaller sub-problems. Then, sensitivity analysis is used to quantify the intensities of the correlations. For problems in which all correlations are weak or there are a mix of weak and strong correlations, the proposed method is very effective in reducing the total number of function evaluations to achieve a similar accuracy. For problems whose correlations are all strong, the proposed method is not be advantageous. An optimization strategy based on iterative metamodel-supported decomposition is proposed in which the decomposition and optimization phases are performed simultaneously and iteratively, in contrast to a one-time decomposition-optimization process. The results show that except for the category of non-decomposable problems with all or lots of strong correlations, the proposed strategy improves the accuracy of the optimization results noticeably. The developed algorithm is applied to a practical engineering problem to test its effectiveness in real-world applications. An optimal assembly planning problem with a 100-dimensional objective function is optimized using the proposed method. Comparison with other optimization methods results and the baseline values shows significant improvement in the obtained optimum with the same number of function calls. The results represent the state-of-the-art for optimization of HEB problems.

Document type: 
Thesis
File(s): 
Supervisor(s): 
G. Gary Wang
Department: 
Applied Sciences:
Thesis type: 
(Thesis) Ph.D.

Aerofoil profile modification effects for improved performance of a vertical axis wind turbine blade

Author: 
Date created: 
2014-10-16
Abstract: 

Due to the growing need of sustainable energy technologies, wind energy is gaining more popularity day by day. For micro power generation vertical axis wind turbine (VAWT) is preferred due to its simplicity and easy to install characteristics. This study investigates the effects of profile-modification on a NACA0015 aerofoil used in VAWTs. The profile-modifications being investigated consist of a combination of inward semi-circular dimple and Gurney flap at the lower surface of the aerofoil. The study also uses a Response Surface Analysis (RSA) based fully automated optimization technique to maximize the average torque produced by the wind turbine blade. The data set used in the RSA optimization is generated using computational fluid dynamics (CFD) simulations. In order to ensure reliability, the model used in the CFD simulations is validated against previous experimental results. The optimized shape of the modified aerofoil is shown to improve in the aerodynamics of the wind turbine blade under both static and dynamic conditions.

Document type: 
Thesis
File(s): 
Supervisor(s): 
Krishna Vijayaraghavan
Department: 
Applied Sciences:
Thesis type: 
(Thesis) M.A.Sc.

Characterization of Strongly Coupled Micro-Resonator Systems for Multi-Sensor Applications

Date created: 
2014-11-13
Abstract: 

The objective of this research is analyzing the behavior of strongly coupled micro-resonating systems. In coupled resonator arrays, the additional degrees of freedom from coupling of the resonators to each other can be employed to enhance the sensitivity and selectivity of the sensor system. In order to achieve this, the effect of coupling strength on sensitivity of the system is investigated. It is shown that sensitivity of the sensor system to perturbations can be increased significantly through proper selection of the coupling coefficient between resonators. To date, the research on coupled resonant sensors has concentrated on weakly coupled systems which mostly depend on measurement of signal amplitudes. Conversely, strongly coupled resonant sensor systems, provide a frequency output with all the advantages of resonant sensing. It is established that by moving to the strongly coupled region, the sensitivity of the coupled system to the input is increased compared to uncoupled resonator systems. Moreover, a method for processing signals from a coupled resonator array is developed which relates the perturbation ratio to the relative change in eigenvalues before and after insertion of perturbation. The method is based on analyzing the relative differences between eigenvalues of the system, which is in contrast to the commonplace methods of focusing on individual modes of a the coupled system. Besides enhanced sensitivity, this property can be employed to reduce the effect of manufacturing tolerances on the sensor system response. The proposed model is experimentally verified using coupled resonator arrays fabricated through in-house and standard micro-fabrication processes

Document type: 
Thesis
File(s): 
Supervisor(s): 
Behraad Bahreyni
Department: 
Applied Sciences:
Thesis type: 
(Thesis) Ph.D.

Development of an interactive engineering design optimization framework

Date created: 
2014-10-29
Abstract: 

Engineering optimization is often completely automated after initial problem formulation. Although purely algorithmic approaches are attractive, keeping the engineer out-of-the-loop also suffers from key drawbacks. First, problem formulation is a challenging task and a poorly formulated problem often causes extra efforts and extended optimization time. Second, stakeholders may not trust the results of an optimization algorithm when presented without context. This thesis uses information visualization to keep designer in-the-loop during design optimization formulation, modeling, optimization, and result interpretation stages. Parallel coordinates is the central representation used, accompanied by two-dimensional projections for navigation and a scatterplot matrix for overview. Methods are presented to split the design and performance spaces into meaningful regions by clustering and by interaction. A new data-mining technique is also presented to find relationships between black-box constraints to remove redundant and unimportant constraints. A software prototype is developed and successfully applied to an automotive assembly optimization problem.

Document type: 
Thesis
File(s): 
Supervisor(s): 
Gary Wang
Department: 
Applied Sciences:
Thesis type: 
(Thesis) M.A.Sc.

Fuel Cell Diagnostics using Electrochemical Impedance Spectroscopy

Date created: 
2014-09-02
Abstract: 

When a proton exchange membrane (PEM) fuel cell runs short of hydrogen, it suffers from a reverse potential fault. This fault, driven by neighboring cells, can lead to anode catalyst degradation and, through cell reversal, to holes in the membrane due to local heat generation. As a result, hydrogen leaks through the electrically-shorted membrane-electrode assembly (MEA) without being reacted, and it recombines directly with air. This recombination results in a reduction in oxygen concentration on the cathode side of the MEA and a fuel cell voltage reduction. Such voltage reduction can be detected by using electrochemical impedance spectroscopy (EIS). In this research, in order to fully understand the effect of this oxygen reduction fault, the impedances of single and multi-cell stacks at different leak rates were measured. Then the impedance signatures were compared with the signatures of stacks having non-leaky cells at different oxygen concentrations with the same current densities. The signatures were analyzed by fitting the leaky stacks and oxygen concentrations impedance data sets with the parameters of a Randles circuit. The correlation between the parameters of the two data sets allows us to understand the change in impedance signatures with respect to a reduction of oxygen in the cathode side. Using the circuit parameters, a model that establishes a relationship between impedance and voltage was also considered. With the help of this model along with the impedance signatures, we are able to detect the reduction of oxygen concentrations at the cathode by using fuzzy logic (FL). However, resolution of detection was reduced with the reduction of leak rate and/or increases in the stack cell-count. The amount of hydrogen leak rates were quantified by simulating the resulting reduced amount of oxygen with the use of neural network (NN) method. Successful implementation of FL and NN methods in a fuel cell system can result in an on-board diagnostics system that can be used to detect and possibly prevent cell reversal failures, and to permit understanding the status of crossover or transfer leaks versus time in operation. Using such system will increase the reliability and performance of fuel cell stacks, where leaks can be detected online and appropriate mitigation criteria can be applied.

Document type: 
Thesis
File(s): 
Supervisor(s): 
Farid Golnaraghi
Department: 
Applied Sciences:
Thesis type: 
(Thesis) Ph.D.

A New Integrated Approach for Modeling Green Passive Cooling Systems

Author: 
Date created: 
2014-08-11
Abstract: 

A new one-dimensional thermal network modeling approach is proposed that can accurately predict transient/dynamic temperature distribution of passive cooling systems. The present model has applications in a variety of electronic and power electronic systems. The main components of any passive cooling solution are heat spreaders, heat pipes, and heat sinks as well as thermal boundary conditions such as natural convection and radiation heat transfer. In the present approach, all the above-mentioned components are analyzed, analytically modeled and presented in the form of resistance and capacitance (RC) network blocks. The proposed RC model is capable of predicting the transient/dynamic as well as steady state thermal behavior of the targeted passive cooling systems with significantly less cost of modeling compared to conventional numerical simulations. Furthermore, the present method takes into account thermal inertia of the system and is capable of capturing thermal lags in various system components under all applicable operating conditions. To validate the proposed model, a number of custom-designed test-beds are also built and a comprehensive experimental study is conducted.

Document type: 
Thesis
File(s): 
Supervisor(s): 
Majid Bahrami
Department: 
Applied Sciences: School of Mechatronic Systems Engineering
Thesis type: 
(Thesis) M.A.Sc.